Lower Prostate Cancer Risk Found in Childless Men

Action Points

Explain to interested patients that this study found that childless men have a reduced risk of prostate cancer but that fathers' risk decreases with each additional child.

Point out that the mechanisms for the reductions were not identified in this study.

COPENHAGEN, Jan. 7 -- Men who have never had children are 16% less likely than fathers to develop prostate cancer, suggested a Danish cohort study.

Contrary to a previous report, though, the sex of offspring of men with children did not affect the fathers' prostate cancer risk (RR: 0.99, 95% CI: 0.90 to 1.08), reported epidemiologist Kristian Jorgensen, M.Sc., of Statens Serum Institut here, and colleagues online in Cancer.

Among fathers, there was a significant trend toward a gradually reduced prostate cancer risk with increasing number of children (P=0.009), a pattern applying to both sons (P=0.01) and daughters (P=0.04). Prostate cancer risk significantly decreased in fathers by 5% with each additional child of either sex (RR: 0.95, 95% CI: 0.91 to 0.99, P=0.009),

The 5% risk reduction was a combined effect of non-observable changes for men with up to four children, a 31% decrease for fathers of five children, and a 43% reduction for those with six or more children.

The researchers suggested the "healthy father" phenomenon, in which patients who remain fertile and able to have more children later in adulthood are less likely to develop cancer, as a possible reason for this effect.

However, citing three well-documented risk factors for prostate cancer -- race, family history of the disease, and age -- and the conflicting results of earlier studies, the authors said that "it remains controversial whether fatherhood status is associated with prostate cancer risk."

Although the mechanism causing the reduction in prostate cancer risk in childless men is unclear, the Danish team suggested it might be related to androgen levels, which "have repeatedly been positively associated with risk of prostate cancer." Infertile men have lower levels of testosterone than fertile men, possibly accounting for the lower risk in childless men.

Jorgensen and colleagues established a cohort of all Danish men born from 1935 through 1988, using data from the national civil registration system. Prostate cancer diagnoses were recorded from April 1, 1968, when the system was created, through 2003.

A total of 3,400 cases occurred during 51.6 million years of follow-up. The median age at diagnosis was 60 for all men.

The 16% risk reduction in childless men (RR: 0.84, 95% CI: 0.73 to 0.95) was calculated after adjusting for age, calendar period, and marital status.

The researchers found no difference in prostate cancer risk between fathers with sons and those with daughters only (RR: 0.99, 95% CI: 0.90 to 1.08), contrary to the findings of a cohort study published last year (J Natl Cancer Inst 2007; 99: 77-81).

Fathers with twins had a nonsignificant 19% decrease in risk compared with fathers without (RR: 0.81, 95% CI: 0.61 to 1.05).

The study was limited by the exclusion of men born before 1935, a consequence, the authors said, of the difficulty in accurately identifying their children prior to that year.

Thus, the researchers did not have any data on patients older than 68.

"We cannot exclude the theoretical possibility that risk estimates could be slightly different if all age groups were included," they wrote.

"Additional studies are required to identify the underlying biologic, environmental, social, and/or behavioral factors that explain the observed differences in prostate cancer risk between fathers and childless men and between men fathering few and those fathering many children," they concluded.

The authors did not report funding information or conflicts of interest.

Reviewed by Zalman S. Agus, MD Emeritus Professor University of Pennsylvania School of Medicine

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